Copolymers and hydrogels: process and articles made thereof

ABSTRACT

Copolymers having improved machining and water resistant properties are produced using a monomer containing an adduct protecting group, particularly an alkyl boronic acid adduct, of glyceryl acrylate or glyceryl methacrylate, in combination with an alkyl acrylate or methacrylate, and optionally a glycidyl acrylate or methacrylate. After machining and shaping, the adduct is removed to provide a hydrogel useful as a contact lens material.

This is a continuation, of application Ser. No. 265,304, filed May 20, 1981, now U.S. Pat. No. 4,401,797.

BACKGROUND

1. Field of the Invention

This invention relates generally to copolymers having improved physical and chemical properties which are produced using a protecting group (adduct), particularly an alkyl boronic acid adduct of glyceryl methacrylate or glyceryl acrylate, in combination with an alkyl acrylate or alkyl methacrylate, and optionally using a crosslinking agent such as a glycidyl acrylate glycidyl methacrylate, polyol diacrylate or polyol dimethacrylate. The copolymer has improved handling, machining and shaping properties with respect to water sensitivity in comparison with related materials. Removal of the adduct, as by treatment with hot water or hydrogen peroxide buffer, produces a hydrogel which is useful as a contact lens material.

2. Prior Art

While glass contact lenses were used to correct vision problems in the early 1900's, widespread use and development of the contact lens field did not occur until the advent of organic polymer chemistry during and after World War II. During this period hard contact lenses were usually made from the polymer, polymethylmethacrylate. Some problems encountered with the use of this polymer as a contact lens material include:

(1) inability of many people to adapt to the presence of a hard lens in the eye;

(2) small particles lodged under the lens cause irritation of the cornea;

(3) after one to five years of use, many people experience discomfort and discontinue use; and

(4) impermeability of the polymer to physiological agents, such as oxygen and carbon dioxide necessary for corneal metabolism.

This last property causes "oxygen starvation" which produces "corneal edema," a serious eye condition which is usually reversible by discontinuing use of the hard contact lens.

In view of the above difficulties, efforts were made to develop new materials which overcome the problems of the hard lens. One class of such lens materials are hydrogels of sparingly cross-linked hydrophilic comonomers, and unsaturated organic acids and diacids, described for example in U.S. Pat. Nos. 2,976,576 and 3,220,960. A specific hydrogel disclosed in these patents is a slightly crosslinked material comprising a major amount of 2-hydroxyethyl methacrylate. This hydrogel has become widely known in the art as "HEMA" and is particularly useful because of its ability to absorb about 35 to 45 percent by weight of water. The water renders the lens permeable to oxygen, and also soft and flexible so as to enable it to conform to the curvature of the eye.

In spite of its obvious advantages, the HEMA lens presented some additional problems, including:

(1) a lack of clarity of central vision because of a constantly changing optical surface resulting from normal eye movement and blinking;

(2) a lack of sufficiently rigid, non-deforming surface which would correct astigmatism;

(3) corneal irritation possibly caused by a lack of tear exchange because the tight lens conformation to the eye prevents flow at the edge of the lens;

(4) an accumulation of catabolic products; and

(5) a lack of structural stability.

Additional polymers and manufacturing techniques to improve the overall properties of contact lenses are disclosed in U.S. Pat. Nos. 3,361,858; 3,542,097; 3,647,736; 3,700,761; 3,728,315; 3,926,892; 4,045,547; 4,095,877; 4,109,070; and 4,113,686.

A new contact lens material has been reported to overcome the problems described above and is disclosed in U.S. Pat. No. 4,056,496, which is incorporated herein by reference. These materials are hydrogels formed from a dihydroxyalkyl acrylate or methacrylate, an alkyl acrylate or methacrylate and optionally a minor amount of an epoxidized alkyl acrylate or methacrylate. The properties of these hydrogels when compared to HEMA are:

(1) stronger and stiffer;

(2) capable of being fabricated of a thinner cross-section;

(3) capable of providing increased pumping action of tears caused by blinking;

(4) substantial oxygen and carbon dioxide permeability needed for normal corneal metabolism;

(5) extended wear--in some cases up to six months;

(6) improved ability to be cleaned; and

(7) a toughness which prevents tearing.

The polymers described in U.S. Pat. No. 4,056,496 on occasion were found to present problems during shaping and machining, probably due to the polymer's ability to absorb water from the atmosphere. Careful control of the humidity during machining was found to be necessary. Further, water based or compatible machining and polishing oils and abrasives could not be used because of their incompatibility with the polymer. Finally, polymers of this type often become seriously distorted after machining when they absorb water necessary to be useful as contact lens materials. Correction of this lens distortion is expensive, time-consuming, and sometimes impossible (resulting in the total loss of previously manufactured polymer material).

It would, therefore, be useful to have a polymeric material which could be easily machined using water based and compatible oils, polishes and abrasives without regard to humidity. This polymer could subsequently be treated to produce a hydrogel material having the desired properties, e.g., minimal distortion, for use as a contact lens material.

SUMMARY OF THE INVENTION

This invention describes a copolymer formulation and method of manufacture to produce a polymeric material which has improved machinability, and resistance to water. When the polymer is treated subsequently with aqueous chemical agents, a hydrogel is produced having the desired characteristics for use as a contact lens. It is of particular significance that the polymer material can be machined with water based agents to the desired shape, then treated to form a hydrogel material which has the desired contact lens properties.

The copolymers hereof include a first monomer which is a hydrophilic monomer selected from the group of dihydroxyalkyl acrylates and methacrylates in which the dihydroxyl groups of the alkyl portion have been chemically treated to form a protecting group (adduct). The adduct is further purified by certain separation techniques including, treatment with aprotic non-hydroxylic solvents.

The second monomer is a substantially water insoluble monomer selected from the group consisting of alkyl acrylates and alkyl methacrylates.

The copolymer may optionally include a third monomer consisting of an epoxidized alkyl acrylate or epoxidized alkyl methacrylate. The copolymer may optionally also include a third monomer which is a polyol diacrylate or polyol dimethacrylate.

The copolymer is formed by a free radical, bulk polymerization in the substantial absence of solvent. After formation the copolymer can be easily machined and shaped in the presence of water and humidity using water-based and water compatible oils, polishes and abrasives known in the art. After shaping, the copolymer is treated, for example with water or hydrogen peroxide in a buffer solution, to remove the adduct to thereby obtain a hydrogel material having the desired contact lens properties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Specifically, this invention concerns a polymer formed by a free radical bulk polymerization of:

(a) a first monomer of the formula: ##STR1## wherein: R₁ is hydrogen or methyl;

m is an integer from 1 to 4;

n is an integer from 0 to 1;

X and Y are independently selected from the group consisting of:

(1) --C(O)OR₂ (alkyl carbonate)

where R₂ is an alkyl group containing from 1 to 8 carbon atoms;

(2) hexahydropyranyl;

(3) where X and Y together form one protecting group selected from the group consisting of ##STR2## wherein: R₃ is a lower alkyl group containing 1 to 6 carbon atoms, cycloalkyl group containing 3 to 6 carbon atoms, and aryl selected from the group consisting of phenyl, tolyl, and naphthyl; ##STR3## wherein: R₄ and R₅ are independently selected from hydrogen and lower alkyl groups containing 1 to 6 carbon atoms, or together may form a cyclic ring containing from 2 to 6 carbon atoms; ##STR4## wherein: R₆ is a lower alkyl group containing from 1 to 6 carbon atoms; and ##STR5##

(b) a second substantially water insoluble monomer of the formula: ##STR6## wherein: R₇ is hydrogen or methyl; and

R₈ is lower alkyl having 1 to 6 carbon atoms or cycloalkyl having from 3 to 6 carbon atoms;

the molar ratio of said first monomer to said second monomer being between about 1:30 and 20:1; and

(c) optionally, a third substantially water insoluble monomer of the formula: ##STR7## wherein: R₉ is hydrogen or methyl; and

p is an integer from 1 to 6;

the concentration of said third monomer when present being between about 0 and 30 percent by weight of the first monomer.

More specifically, said polymer includes as

(a) first monomer a compound of the formula: ##STR8## wherein: B is a boron atom;

R₁ is hydrogen or methyl;

R₃ is lower alkyl containing 1 to 6 carbon atoms or cycloalkyl having 3 to 6 carbon atoms or aryl selected from the group consisting of phenyl, tolyl and naphthyl; m is an integer from 1 to 4; and n is an integer from 0 to 1; and

the second and third monomers are defined above.

The first monomer described herein may be prepared by treatment of the dihydroxyalkyl acrylate or methacrylate of the formula ##STR9## wherein: R₁, m and n are as defined above,

with a suitable compound(s) to obtain protection of both of the adjacent hydroxyl groups by formation of a five- or six-membered ring structure.

Such compounds and the protecting groups formed therefrom are shown in the following table, wherein R₂, R₃, R₄, R₅ and R₆ are as defined above and n is zero.

    ______________________________________                                         Compound    Protecting Group Adduct                                            Name/Structure                                                                             Name        Structure                                              ______________________________________                                          ##STR10##  Isopropylidine                                                                              ##STR11##                                              ##STR12##  Ketal                                                                                       ##STR13##                                             Carbonyl Chloride/ COCl.sub.2                                                              Cyclic Carbonate                                                                            ##STR14##                                              ##STR15##  Acetal                                                                                      ##STR16##                                             Thionyl chloride/ SOCl.sub.2                                                               Cyclic sulfite                                                                              ##STR17##                                             Tetrahydropyran/                                                                           Tetrahydro- pyranylether                                                                    ##STR18##                                              ##STR19##  Alkyl carbonate                                                                             ##STR20##                                             Alkyl or aryl boronic acid/ R.sub.3B(OH).sub.2                                             Alkyl or aryl boronic acid adduct                                                           ##STR21##                                             Alkyl or aryl boronic halide/ R.sub.3BX.sub.2                                              Alkyl or aryl boronic acid adduct                                                           ##STR22##                                             Dialkyl Carbonylchloride R.sub.2 R.sub.2 NC(O)Cl                                           Dialkyl Urethane                                                                            ##STR23##                                             ______________________________________                                    

Analogous structures are produced when n is n is 1. The use of certain of such compounds to protect hydroxyl groups in steroid chemistry has been discussed by Carl Djerassi, in "Steroid Reactions," published by Holden-Day, Inc., in 1963, pages 67-88. The preparation of protected acrylates and methacrylates is also discussed in U.S. Pat. No. 2,680,735 and British Pat. Nos. 690,709 and 852,384.

Preferably, the compound used to form the protecting group (adduct) is the alkyl or aryl boronic acid because of its ease of addition and later removal under mild conditions, such as heating in water, treatment with dihydroxyl alkanes in water with heating, treatment with dilute hydrogen peroxide in a buffer solution at ambient temperature, and treatment with a sodium perborate solution. More preferably, the compounds used to protect the adjacent hydroxyl grups are alkyl boric acids, including:

methyl boronic acid

ethyl boronic adcid

n-propyl boronic acid

isopropyl boronic acid

n-butyl boronic acid

isobutyl boronic acid

sec-butyl boronic acid

cyclobutyl boronic acid

n-pentyl boronic acid

isopentyl boronic acid

neopentyl boronic acid

cyclopentyl boronic acid

n-hexyl boronic acid

isohexyl boronic acid and

cyclohexyl boronic acid,

phenyl boronic acid,

o-, m-, or p-tolyl boronic acid,

naphthalyl boronic acid, and mixtures thereof.

The preferred protecting agent at this time, the compound used to protect the hydroxyl groups, is butyl boronic acid.

The dihydroxy adduct of the formula: ##STR24## wherein: R₁, X, Y, m and n are as described above,

is subsequently treated with an aprotic nonhydroxylic solvent. The adduct is soluble in said solvent or mixtures of solvents whereas impurities, such as the unreacted or partially reacted dihydroxy compounds, are insoluble and may be separated by standard techniques, such as extraction and crystallization. The solvent is then removed by evaporation and the purified adduct is ready for copolymerization. Aprotic, nonhydroxylic solvents useful in this separation step include the following:

n-pentane

cyclopentane

n-hexane

cyclohexane

n-heptane

cycloheptane

n-octane

cyclooctane

isooctane

diethyl ether

mineral spirits and

those other solvents and mixtures of solvents known in the art to be useful to separate polar compounds from nonpolar compounds. The presently preferred solvents are n-pentane and n-hexane.

The purified alkyl boronic acid adduct of glyceryl methacrylate has been observed to autopolymerize at room temperature. This monomer should be mixed and polymerized immediately after preparation or stabilized using organic amines, such as cyclohexylamine, and retained in the cold.

The second monomer, which is substantially insoluble in water, is of the formula: ##STR25## wherein: R₃ and R₄ are as set forth above.

The molar ratio of said first monomer to said second monomer is between 1:30 and 20:1. Preferbly, the molar ratio of said first monomer to said second monomer is between 1:1 and 10:1. More preferably, the molar ratio of said first monomer to said second monomer is between 1.2:1 and 2:1.

The optional third substantially water insoluble monomer is of the formula: ##STR26## wherein: R₉ and p are as set forth above.

The concentration of this optional third monomer when present by addition may vary between 0.001 and 30% by weight of the first monomer. Preferably, this optional third monomer is glycidyl methacrylate wherein R₉ is methyl and p is 1.

Alternatively, the optional third monomer when present is a substantially insoluble polyol diacrylate or dimethacrylate of the formula: ##STR27## wherein: R₁₀ and R₁₁ are independently selected from methyl and hydrogen; and q is an integer from 0 to 5.

The concentration of this alternative third monomer when present may vary between 0.001 and 30% by weight of the first monomer. Preferably, the third monomer is tetraethyleneglycoldimethacrylate, wherein R₁₀ and R₁₁ are methyl and q is 4, or ethyleneglycoldimethacrylate, wherein R₁₀ and R₁₁ are methyl and q is 1.

Additional third monomers which may be used to achieve the desired properties include, but are not limited to the following:

Methacrylic acid, P0 N-Vinyl-2-pyrrolidone,

Hydroxyalkyl esters of acrylic acid,

Hydroxyalkyl esters of methacrylic acid, and

Trimethylolpropane.

The first, second, and third monomers are combined and bulk polymerized using a free radical catalyst. Such free radical catalysts are well known in the art and include the following:

azobisisobutyrylnitrile (AIBN)

tert-butyl peroxypivalate

tert-butyl peroxydecanoate

tert-butyl perbenzoate

isopropyl peroxydicarbonate

acetoxy peroxide

benzoyl peroxide

2,5-dimethyl-2,5-bis(2-ethyl hexoyl peroxy)hexane

cyclohexanone peroxide

di-sec-butyl peroxydicarbonate

and the like. A presently preferred catalyst is azobisisobutyrylnitrile. The catalyst is present in amounts effective to achieve the desired degree of polymerization. Concentrations which have proved useful are between 0.001 and 1 percent by weight of the first monomer.

The polymer thus obtained is hard and resistant to water in comprison to HEMA and similar non-protected hydrogel polymers. It may be handled, machined and shaped in an atmosphere without special precautions to remove humidity. Further, it may be machined and shaped using water based and water compatible oils, polishes and abrasives. Lens polishing compounds such as EXPAL, which is a finely ground aluminum oxide powder available from the W. R. Grace Co., Inc. may be used, with these polymers in a water solution. Other finely ground metal or metal oxide powders in water are also useful.

The copolymer thus prepared by this free radical polymerization before, or preferably after machining and shaping, may be further treated with water and dilute acid to remove the protecting group and generate the hydroxyl groups. Specific methods to regenerate the hydroxyl groups are described in Steroid Reactions by Djerassi as described above and references cited therein. Preferably, the protecting group is an alkyl boronic acid which typically requires mild reaction conditions for removal, thus, the polymer structure is essentially not affected.

The copolymer prepared by the free radical polymerization process, before, or preferably after machining, and shaping, also may be treated with a dihydroxyalkane and water with boiling to remove the boronic protecting group and produce the hydrogel.

Alternatively, the boron protecting group may be removed by treatment with dilute hydrogen peroxide in a buffer solution. Preferably, the concentration of the hydrogen peroxide is between 0.1 and 20% by weight of the buffer solution. More preferably, the hydrogen peroxide concentration is about 10%.

Typically, the reaction is run between 0° C. and 100° C. at ambient conditions (about 20° C. at standard atmospheric pressure).

Alternatively, a 10% sodium perborate solution may be used to replace hydrogen peroxide in the aforementioned treatment to remove the boron protecting group.

The polymer thus obtained by removal of the protecting group will have a linear expansion of about 5-20 percent and more likely 6-12%, when it is hydrated to become a hydrogel. The water of hydration of the hydrogel will be between about 20 to 45 percent by weight.

EXAMPLES

The following examples are given to enable those skilled in this art to more clearly understand and practice the present invention. They should not be considered as a limitation upon the scope of the invention but merely as being illustrative and representative thereof.

EXAMPLES 1-4

The compounds shown in the following table are used to protect the hydroxyl groups. The following general synthetic procedure is used.

Anhydrous Compound A (about 1.1 moles) is treated with about 160 grams (g) of dried glyceryl methacrylate (about 1 mole) in an ice bath without solvent in a nitrogen atmosphere. The reaction occurs over two hours after which the water produced is either removed by azeotropic distillation with toluene (Example 1), or by using 20-30 g of anhydrous sodium sulfate (Example 3). In Examples 2 and 4 pyridine, about 2 equivalents, is used to react with the hydrogen chloride which is generated. The toluene is removed using reduced temperature and pressure, about 100 milliliters (ml) of hexane is added, and the product is filtered. The residue is washed twice with 20 ml of hexane, filtered and combined with the hexane extracts. The reaction mixture is kept cold and under nitrogen. The hexane solution is evaporated under vacuum to produce the adduct product.

    ______________________________________                                                            Product                                                                        W is                                                        Compound A         CH.sub.2C(CH.sub.3)C(O)OCH .sub.2                           Example                                                                               Structure   (g)     Structure   (g)                                     ______________________________________                                         1      CH.sub.3 C(O)CH.sub.3.sup.a                                                                 64                                                                                     ##STR28##  150                                     2      COCl.sub.2.sup.b                                                                           110                                                                                     ##STR29##  157                                     3      HC(OC.sub.2 H.sub.5).sub.3.sup.a                                                           135                                                                                     ##STR30##  160                                     4      SOCl.sub.2  132                                                                                     ##STR31##  159                                     ______________________________________                                          .sup.a 0.5 percent by weight of anhydrous sulfuric acid is used as a           catalyst.                                                                      .sup.b as a gas                                                          

Sixty grams of the adduct is then combined with 40 g of methyl methacrylate and 0.50 g of tert-butyl peroxy pivalate as catalyst in a glass tube at 70° C. for 3 hr. The resulting polymers are hard and water resistant as compared to HEMA. After machining and shaping each polymer in the form of a contact lens in a humid environment, each lens is treated with a 1% solution of hydrochloric acid at room temperature for 24 hours and then at 50° C. for 2 hours. Each polymer is examined for percent elongation and for percent of water of hydration. The results are shown in the following table:

    ______________________________________                                                              Hydrogel                                                         Precursor Compound to Produce                                                                      %         %                                         Example                                                                               Protecting Group    Elongation                                                                               Water                                     ______________________________________                                         1      CH.sub.3 C(O)CH.sub.3                                                                              10        37                                        2      SOCl.sub.2           8        21                                        3      HC(OC.sub.2 H.sub.5).sub.3                                                                         12        44                                        4      SOCl.sub.2           9        30                                        ______________________________________                                    

These materials are colorless or slightly yellow and are useful as contact lens materials.

EXAMPLE 5

To a 250 ml round bottom flask cooled to 0° C. using an ice bath is added 33.8 g of glyceryl methacrylate (0.211 moles, from commercial sources) which was previously dried using anhydrous sodium sulfate. Without solvent and under a nitrogen atmosphere, 25.0 g of n-butyl boronic acid (0.245 moles, from commercial sources) is added. After mixing, 0.05 ml of commercial cyclohexyl amine is added as a stabilizer. The reaction mixture is stirred for 30 minutes during which time about 20 g of sodium sulfate is added in three portions. All subsequent steps are performed cold and under a nitrogen atmosphere. Excess hexane (about 100 ml) is added and the hexane extract is filtered. The residue is washed twice with 20-ml of hexane, filtered and added to the initial hexane extract and filtered twice more. The hexane solution is removed under vacuum to produce 47.0 g of the butyl boronic acid adduct of glyceryl methacrylate, about 98% of the theoretical yield. As a stabilizer, 0.05 ml of additional cyclohexylamine is added to the product.

EXAMPLE 6A

A polymerization mixture of 34.6 g of the butyl boronic acid adduct of glyceryl methacrylate of Example 5, 10.1 g of methylmethacrylate and 0.044 g of azobisisobutyrylnitrile (AIBN) as catalyst are combined.

A 32.1 g portion of the polymerization mixture is put in a polyethylene mold and heated at 70°-75° C. for one hour and then retained at room temperature overnight (about 16-20 hr). A colorless polymer rod is obtained. The rod is cut into buttons which are easily cut into the shape of a contact lens using standard techniques. The lenses are treated overnight with about 100 ml of 10% hydrogen peroxide in a sodium bicarbonate buffer solution (about pH 9). These lenses are further hydrated in saline solution to complete the formation of the hydrogel. These hydrogel lenses are useful as contact lenses.

EXAMPLE 6B

A 12.6 gram portion of the polymerization mixture prepared in Example 6 is placed in a polypropylene test tube for 36 hours at room temperature, then heated at 60° C. for four hours. A polymer rod is obtained from which lenses could be easily shaped under humid conditions. The lens is treated with 10% hydrogen peroxide in a sodium bicarbonate buffer solution overnight to obtain the hydrogel useful as a contact lens material.

EXAMPLE 6C

The lens prepared in Example 6B is further hydrated in saline solution to obtain the hydrogel. The polymeric hydrogel is useful as a contact lens material.

EXAMPLES 7-21

The butyl boronic acid adduct is prepared according to Example 5. Abbreviations for the components used to prepare the polymer are butyl boronic acid adduct of glyceryl methacrylate, BBA-GMA; and methyl methacrylate, MMA. The percentages of each component are shown in the following table:

    ______________________________________                                                BBA-GMA   MMA      Crosslinking                                                Weight    Weight   Agent      Hydration                                 Example                                                                               Percent   Percent  Weight Percent                                                                            % H.sub.2 O                               ______________________________________                                          7     100       --       --         .sup.a                                     8     80        20       --         --                                         9     60        40       --         44                                        10     50        50       --         36                                        11     40        60       --         24                                        12     30        70       --         --                                        13     80        10       10.sup.b   --                                        14     69        29       2.sup.b    --                                        15     69        29       2.sup.c    --                                        16     59        39       2.sup.b    --                                        17     59        39       2.sup.c    --                                        18     49        49       2.sup.b    --                                        19     49        49       2.sup.c    --                                        20     39        59       2.sup.b    --                                        21     39        59       2.sup.c    --                                        22     10        80       10.sup.b   --                                        ______________________________________                                          .sup.a Not useful as a contact lens                                            .sup.b Diethyleneglycol                                                        .sup.c Tetraethyleneglycol dimethacrylate                                

The components shown above are combined according to the procedure described in Example 5. The clear polymers obtained are not particularly sensitive to humidity and are cut using water based and compatible oils, polishes, and abrasives. The lenses obtained were then treated by one of the following methods to remove the butyl boronic acid adduct, produce the hydroxyl groups, and partially or completely hydrate the polymer:

Sodium perborate--The lenses are treated with a solution of 10% sodium perborate for about 24 hours at room temperature;

Hydrogen Peroxide--The lenses are treated with 10% hydrogen peroxide in a sodium bicarbonate buffer solution (about pH 9) for 16-24 hours at room temperature;

Dihydroxypropane--The lenses are treated with a 20% solution of dihydroxypropane and water and boiled for two hours; or

Water--The lenses are treated with water and boiled for about 8 hours.

After treatment, all lenses are rinsed, boiled in water, and finally hydrated and stored in a saline solution. The water of hydration is shown in the above table.

While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in this art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adopt a particular situation, material, or composition of matter, process, process step or steps, or then present objective to the spirit of their invention without departing from its essential teachings. 

What is claimed is:
 1. A process for making a hydrogel contact lens, comprising the steps of:(A) forming a button from a polymer material, said polymer material being a free radical bulk polymerization product of:(a) a first monomer of the formula: ##STR32## wherein: R₁ is hydrogen or methyl; m is an integer from 1 to 4; n is an integer from 0 to 1; and X and Y are protecting groups and are independently selected from the group consisting of:(1) --C(O)OR₂ wherein R₂ is an alkyl group containing from 1 to 8 carbon atoms;(2) hexahydropyranyl; and (3) where X and Y together form one protecting group, selected from the group consisting of: ##STR33## wherein R₃ is a lower alkyl group containing 1 to 6 carbon atoms, cycloalkyl group containing 3 to 6 carbon atoms; and aryl selected from the group consisting of phenyl, tolyl and naphthyl; ##STR34## wherein R₄ and R₅ are independently hydrogen and lower alkyl groups containing from 1 to 6 carbon atoms and together may form a cyclic ring containing from 2 to 6 carbon atoms; ##STR35## wherein R₆ is a lower alkyl group containing from 1 to 6 carbon atoms; and ##STR36## (b) a second, substantially water insoluble monomer of the formula: ##STR37## wherein: R₇ is hydrogen or methyl; and R₈ is lower alkyl having 1 to 6 carbon atoms or cycloalkyl having from 3 to 6 carbon atoms; the molar ratio of said first monomer to said second monomer being between about 1:30 and 20:1; and, optionally, (c) a third, substantially water insoluble monomer of the formula: ##STR38## wherein: R₉ is hydrogen or methyl; and p is an integer from 1 to 6; or of the formula: ##STR39## wherein: R₁₀ and R₁₁ are independently hydrogen or methyl, and q is an integer from 0 to 5; the concentration of said third monomer, when present, being between about 0 and 30 percent by weight of the first monomer; (B) machining, shaping and polishing said button into the shape of a contact lens, using water compatible oils, abrasives and polishes; and (C) removing said protecting group(s) from said polymer button, as formed into the shape of a contact lens, by chemical means and replacing said protecting group(s) with hydroxyl groups.
 2. The process of claim 1 for making a hydrogel contact lens, wherein said protecting group(s) are removed by treating said polymer button, as formed into the shape of a contact lens, with boiling water.
 3. The process of claim 1 for making a hydrogel contact lens, wherein said protecting group(s) are removed by treating said polymer button, as formed into the shape of a contact lens, with a dilute aqueous acid solution.
 4. The process of claim 1 for making a hydrogel contact lens, wherein said protecting group(s) are removed by treating said polymer button, as formed into the shape of a contact lens, with hydrogen peroxide in a buffer solution.
 5. The process of claim 1 for making a hydrogel contact lens, comprising the additional step of:(D) hydrating said polymer button, as formed into the shape of a contact lens, after said protecting group(s) have been removed.
 6. A hydrogel contact lens made according to the process of claim
 1. 7. A hydrogel contact lens made according to the process of claim
 2. 8. A hydrogel contact lens made according to the process of claim
 3. 9. A hydrogel contact lens made according to the process of claim
 4. 10. A hydrated hydrogel contact lens made according to the process of claim
 5. 11. The process of claim 1 for making a contact lens, wherein said polymer material is first formed into a rod from which said button is then formed.
 12. A process for making a hydrogel contact lens, comprising the steps of:(A) forming a button from a polymer material, said polymer material being a free radical bulk polymerization product of:(a) a first monomer of the formula: ##STR40## wherein: R₁ is hydrogen or methyl; m is an integer from 1 to 4; n is an integer from 0 to 1; and X and Y are protecting groups and are independently selected from the group consisting of:(1) --C(O)OR₂ wherein R₂ is alkyl group containing from 1 to 8 carbon atoms; (2) hexahydropyranyl; and (3) where X and Y together form one protecting group, selected from the group consisting of: ##STR41## wherein R₃ is a lower alkyl group containing 1 to 6 carbon atoms, cycloalkyl group containing 3 to 6 carbon atoms; and aryl selected from the group consisting of phenyl, tolyl and naphthyl; ##STR42## wherein R₄ and R₅ are independently hydrogen and lower alkyl groups containing from 1 to 6 carbon atoms and together may form a cyclic ring containing from 2 to 6 carbon atoms; ##STR43## wherein R₆ is a lower alkyl group containing from 1 to 6 carbon atoms; and ##STR44## (b) a second, substantially water insoluble monomer of the formula: ##STR45## wherein: R₇ is hydrogen or methyl; and R₈ is lower alkyl having 1 to 6 carbon atoms or cycloalkyl having from 3 to 6 carbon atoms; the molar ratio of said first monomer to said second monomer being between about 1:30 and 20:1; and, optionally, (c) a third, substantially water insoluble monomer of the formula: ##STR46## wherein: R₉ is hydrogen or methyl; and p is an integer from 1 to 6; or of the formula: ##STR47## wherein: R₁₀ and R₁₁ are independently hydrogen or methyl, and q is an integer from 0 to 5; the concentration of said third monomer, when present, being between about 0 and 30 percent by weight of the first monomer; and (B) machining, shaping and polishing said button into the shape of a contact lens, using water compatible oils, abrasives and polishes.
 13. A hydrogel contact lens comprising the polymer button of claim
 12. 14. The process of claim 12 for making a hydrogel contact lens, comprising the additional step of:(C) removing said protecting group(s) from said polymer button, as formed into the shape of a contact lens, by chemical means and replacing said protecting group(s) with hydroxyl groups.
 15. A hydrogel contact lens made according to the process of claim
 14. 16. A process for making a hydrogel contact lens, comprising the steps of:(A) forming a button from a polymer material, said polymer material being a free radical bulk polymerization product of:(a) a first monomer of the formula: ##STR48## wherein: R₁ is hydrogen or methyl; m is an integer from 1 to 4; n is an integer from 0 to 1; and X and Y together form one protecting group, selected from the group consisting of: ##STR49## wherein R₄ and R₅ are independently hydrogen and lower alkyl groups containing from 1 to 6 carbon atoms and together may form a cyclic ring containing from 2 to 6 carbon atoms; (b) a second, substantially water insoluble monomer of the formula: ##STR50## wherein: R₇ is hydrogen or methyl; and R₈ is lower alkyl having 1 to 6 carbon atoms or cycloalkyl having from 3 to 6 carbon atoms; the molar ratio of said first monomer to said second monomer being between about 1:30 and 20:1; (B) machining, shaping and polishing said button into the shape of a contact lens, using water compatible oils, abrasives and polishes; and (C) removing said protecting group(s) from said polymer button, as formed into the shape of a contact lens, by chemical means and replacing said protecting group(s) with hydroxyl groups. 